The proposal is legally questionable and would not aid the nation’s efforts to fight the coronavirus. More than 5 million Americans have already been diagnosed with COVID-19, making the U.S. home to the world’s worst outbreak.

President Donald Trump is considering a new proposal that would give border officials the unprecedented power to block American citizens and permanent residents from returning to the United States from abroad if they are suspected of being infected with the coronavirus. 

The prospective rule, first reported by the New York Times, has already come under intense scrutiny from legal experts, who question the Trump administration’s authority to block citizens and permanent residents from returning to their home country. 

The effectiveness of such a measure has also come into question, as widespread community transmission has been occurring in the U.S. for five months. More than 5 million Americans have been diagnosed with COVID-19, making the U.S. home to the world’s worst outbreak. Instead, immigration advocates say, the rule represents just the latest attempt by the Trump administration to use the virus to institute temporary border restrictions that could become permanent. 

Trump has previously imposed wide-ranging immigration rules that ban international citizens from entering the U.S., citing the risk of such travelers spreading the virus. But American citizens and permanent legal residents have been exempted from such rules and bans—until now. 

This new proposal would primarily affect the nation’s land crossing along the southern border. However, the policy will also impact travelers arriving in the U.S. on international flights as well as border crossings with Canada (which are currently limited to essential travelers). Mexico is one of the few countries that still allows leisure tourists from the U.S. to visit, and flights between the nations are still operating. Additionally, legal U.S. residents who have visited their home countries and are returning to the U.S could be subject to these new border control protocols. Trump’s order could cause even more confusion at airports as those citizens and legal residents try to re-enter the U.S. from countries where COVID-19 outbreaks are less severe. 

The move would mark the first time Trump has applied immigration restrictions to the hundreds of thousands of U.S. citizens and legal residents who cross the U.S-Mexico land border legally every day. The administration previously restricted nonessential travel, but those have typically not applied to Americans crossing the border for school, work, business or medical appointments.

Trump has repeatedly complained about the Mexican land border as a source of the coronavirus, even as scientists have determined that travelers from Europe were responsible for the spring New York City outbreak that seeded the virus through much of the U.S. While outbreaks along the border in Arizona and Texas have grown in recent months, experts agree that there is little evidence of border crossings driving the spread. 

“I don’t think there’s any evidence that Mexico has anything to do with case increases and hospitalization increases in those areas [along the border],” Dr. Amesh Adalja, an infectious disease physician at the Johns Hopkins University Center for Health Security, told FactCheck. “There’s no evidence of that.”

But the draft of the proposal, parts of which were obtained by The New York Times, cites the spread of COVID-19 in Mexico as evidence of the rule’s necessity. “As noted, the stress that COVID-19 has placed on the Mexican health care system has driven U.S. citizens, L.P.R.s and others from Mexico into the United States to seek care,” the draft of the regulation says.

The draft of the proposal vaguely states that any order blocking citizens and legal permanent residents must “include appropriate protections to ensure that no constitutional rights are infringed,” and emphasizes that citizens and legal residents cannot be blocked altogether—only on a case-by-case basis. Still, legal experts remain unconvinced of the rule’s legality.

“Barring American citizens from the United States is unconstitutional,” Omar Jadwat, the director of the American Civil Liberties Union’s Immigrants’ Rights Project, said in a statement. “The Trump administration has rolled out one border ban after another—most recently on children and asylum seekers—using COVID-19 as an excuse, while failing abysmally to get the virus under control in the United States. The rumored order would be another grave error in a year that has already seen far too many.”

To immigration advocates like Jadwat, the rule represents another Trump administration attempt to take the advantage of the pandemic to implement immigration restrictions that will outlive the virus itself.

Citing the pandemic, Trump has implemented a strict system at the border that immediately turns away most asylum seekers, forcing them to return to Mexico to await processing. The administration has also suspended the issuance of green cards and many work visas through the end of the year, and made it impossible for newly-enrolled international college students to enter the U.S. if their schools are operating entirely online for the fall semester.

While those are all now official policies, it remains unclear whether the administration’s latest proposal will be implemented. Federal agencies were asked to submit feedback on the proposal to the White House by Tuesday, the Times reported. The timeline for any approval remains unknown.